cmb2001 Posted October 29, 2018 Share Posted October 29, 2018 Hi, Preface: I kind of browsed the forum but couldn't find anything matching my problem. I bought a Spider Valve HD100 Mk1 to use while my main amp is being serviced. The seller went through the paces with the amp and informed me the master volume didn't work. being as it was super loud and controllable through channel volume I still bought it. I plan on keeping it as a backup so id like to see if I can fix this issue. Issue: Master Volume sounds to be at about 7 id say compared to other 100 watt amps ive used. I can turn the knob from 0 - 10 and no change in volume, no static, zero response. The volume can be controlled by the channel volume but switching presets will blow ears out if not careful. Could this be remedied by a simple pot change or could it be something more. Looking on suggestions on troubleshooting the circuit maybe? I have some electronics experience so I know about high voltages etc going into the amp. Thanks Quote Link to comment Share on other sites More sharing options...
psarkissian Posted October 29, 2018 Share Posted October 29, 2018 1) What are the brand and numbers of the tubes? 2) Are the speakers connected to the correct outputs for the speakers being used? They have to be impedance matched. 3) Are you using proper speaker cable and not guitar cable to connect the speakers? That also goes to impedance matching issues. Quote Link to comment Share on other sites More sharing options...
cmb2001 Posted October 29, 2018 Author Share Posted October 29, 2018 1. The amp is not with me, I do remember they are ruby 6l6 tubes on output, 12ax7s are unknown brand at this time, I was told it was freshly tubed and biased about a month ago. 2 & 3: the cab is 16 ohm and a speaker cable is in the 16 ohm tap. the amp sounds good its just the master volume does nothing. the channel volume controls the volume on active setting. Quote Link to comment Share on other sites More sharing options...
psarkissian Posted October 29, 2018 Share Posted October 29, 2018 Power tubes should be Sovtek 5881WXT, not Ruby 6L6. The standard spec biasing won't work with these tubes in this amp. The characteristic curves are close, but not close enough, so using our standard biasing will throw things off. These aren't the all analog amps of the 1960's, the digital board and analog sections need to talk to play nice with each other, not using specified parts has an affect. Check my post here on this subject,.... Quote Link to comment Share on other sites More sharing options...
cmb2001 Posted October 29, 2018 Author Share Posted October 29, 2018 ill double check on the actual tube number tonight. I know its hard to say without the amp in front of you, but in your opinion, if they are 6l6 could components in the amp be damaged or could replacing the 6l6 with sovtek 5881s remedy the problem? Quote Link to comment Share on other sites More sharing options...
psarkissian Posted October 29, 2018 Share Posted October 29, 2018 Not my opinion, my experience and being an old guy who's been dealing with tubes a long time. Dealt with Spider Valve from its beginning. Dealing with tube gear in general since I was a teen. Have the 5881WXT match quartet installed and biased by a Line 6 authorized service center with the correct info. 12AX7B China or 12AX7EH is fine. Quote Link to comment Share on other sites More sharing options...
cmb2001 Posted October 29, 2018 Author Share Posted October 29, 2018 I meant in your opinion is it possible the difference between 6l6 and 5881 tubes can physically damage the internal components of the amp or if I put sovtek 5881 tubes as suggested the master volume should work? Quote Link to comment Share on other sites More sharing options...
psarkissian Posted October 29, 2018 Share Posted October 29, 2018 Yes. It does cause problems with internal circuitry if let go for too long. Have had several on my bench in the past. 1 Quote Link to comment Share on other sites More sharing options...
indyj_son Posted January 28, 2020 Share Posted January 28, 2020 I had a similar problem with a master volume being scratchy and sketchy at lower volumes. i had to set it at about 50% to calm things down. I then put and external volume control pot in the effects loop to control the level of the signal getting to the power section. It seems to work OK but what I've read from your comments I am starting to think maybe this is a bad idea... Quote Link to comment Share on other sites More sharing options...
indyj_son Posted January 28, 2020 Share Posted January 28, 2020 On 10/29/2018 at 2:56 PM, psarkissian said: Yes. It does cause problems with internal circuitry if let go for too long. Have had several on my bench in the past. I had a similar problem with a master volume being scratchy and sketchy at lower volumes. i had to set it at about 50% to calm things down. I then put and external volume control pot in the effects loop to control the level of the signal getting to the power section. It seems to work OK but what I've read from your comments I am starting to think maybe this is a bad idea... Quote Link to comment Share on other sites More sharing options...
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